And theirs is not the only health at risk, given recent news that the world's citizens could be ingesting on average a credit-card worth of plastic a week. These issues are so immense and so implacably interconnected you have to wonder whether this forced hypocrisy isn’t a factor also in the current, climate-exacerbating global epidemics of obesity, narcissism and depression.

Filmmaker Damon Gameau planting a tree with his wife and daughter.Credit:

2040 is not a sophisticated film. Nor is it original, the ideas and arguments all having been developed by others. It’s not meant to be either of those things – being firmly targeted on the practicable solution and the popular middle-brow. Engaging, persuasive and urgent, it’s an exercise in what you might call muscular hope.

Gameau, you recall, made That Sugar Film (2014), where he consumed 40 teaspoons of sugar a day and reported back on his weight gain and fatty liver. Here, he wants to save the world, or at least make it fit for his four-year old daughter to inhabit as a young adult in 2040.

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But it’s less fluffy than that. Most current prophecies go straight to gloom; the sea-level rise, mass migration, global epidemic and war attending climate emergency. Gameau flips it around - asking, rather, what it would take to avoid this.

Answer: not just “mitigation”, and not even just reduction or stabilisation of greenhouse emissions. Atmospheric greenhouse gases, having hovered between 80-280ppm for hundreds of millennia, are now 500ppm. This is uncharted territory. As one commentator notes, even if we reduce emissions enough to stabilise atmospheric GHGs at current levels, we’re still toast.

Illustration: Simon LetchCredit:

Paul Hawken, of the global Project Drawdown, puts it another way. If you’re heading for the cliff, he says, slowing down doesn’t help. You actually have to turn around. We need reversal. We need atmospheric GHGs to start dropping.

How to achieve this by 2040 is the film’s guiding question. Here Gameau applies a further discipline. The world of eco-commentary operates on a knife edge: if you’re critical of government policy, you’re derided as an Eeyore; constructive, you’re a nutty utopian. Gameau dances the middle path, outlining the intractable issue (carbon from transport, waste, farming, energy and ignorance) before focusing exclusively on solutions that deploy existing technology. Things that are doable.

The film documents Gameau’s global search for replicable answers that are already, in some way, at work.

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First, energy. In a tiny impoverished Bangladeshi village, far from the grid, people rely on kerosene for cooking and lighting, with the associated risks of lung disease. A young engineer bowls up with a brilliant invention by SolShare that enables decentralised peer-to-peer solar microgrids. For the price of a shanty-roof panel, a battery and a SolShare box, a household can generate clean energy, sell or give it to the neighbours and, incrementally, build a local, hyper-efficient grid with no ongoing costs, health risks or carbon.

Suddenly people who’ve never had landlines can power mobile phones, night-time economies, Netflix, restaurants, café culture. Where a top-down grid costs billions to build, empowers only corporations and is probably impossible, a local, incremental clean-energy grid bestows community pride, hope to the indigent (who can buy a stand-alone box to power a single fridge or lightbulb) and individual empowerment well beyond the simply literal.

Next up, transport. With up to two-thirds of cities taken by parking and roads, solar-powered autonomous vehicles will not only decimate the 20 per cent GHG emissions that come from transport but because the cars can drive more closely and stack offsite they will liberate vast tracts for carbon-sequestering urban forests and agriculture. With the vanishing demand for oil, further, huge oil fields will also offer sites for afforestation.

Damon Gameau made his name with the documentary That Sugar Film.Credit:

But because we must not only stop producing carbon but actively suck it up, sequestration becomes critical – and here food production is key. Land-farming and sea-farming. Regenerative farming, says Paul Hawken, instigator of the global climate-change offensive Project Drawdown, is a “twofer”. Not only does it cease agricultural emissions, it also sequesters carbon.

Grasslands all over the world, says Gulgong-based farming guru Colin Seis, have been sustained by “large mobs of grazing animals kept moving by predators”. Mimicking these patterns – instead of applying soil-compacting chemical fertilisers – can dramatically increase soil carbon, where each 1 per cent increase can expand water-holding by a staggering 168,000 litres/ha. Take that to your next drought.

Then there’s the sea. The oceans are now so warm and so acidic that fish are dying and molluscs cannot form shells. Marine permaculture proposes thousands of cultivated seaweed forests that, growing perhaps 50 centimetres a day, sequesters potentially billions of tonnes of carbon (restoring the ocean’s alkalinity), provides food, generates jobs, yields fertiliser and biofuel.

Its most surprising is the thought that the sixth most effective weapon (of a hundred) against climate change is educating girls. Although our universities may still regard feminism as the enemy, educating girls is worth 105 gigatons of Co2 due to its effect on fertility, population growth and land management. Go girls!

Elizabeth Farrelly is a Sydney-based columnist and author who holds a PhD in architecture and several international writing awards. She is a former editor and Sydney City Councilor. Her books include 'Glenn Murcutt: Three Houses’, 'Blubberland; the dangers of happiness’ and ‘Caro Was Here’, crime fiction for children (2014).